The present invention relates to piston-glide shoe combinations for use in zone-adjustable variable-crown rolls.
A zone-adjustable variable-crown roll comprises a stationary central axle on which a cylindrical roll mantle is rotatably mounted. A series of piston-glide shoe combinations are generally situated between the axle and the inner surface of the roll mantle and are loaded by hydraulic pressure fluid so that the glide shoes are loaded against the inner surface of the roll mantle to control the distribution of the nip pressure in a nip formed by the variable-crown roll and a counter-roll.
Various constructions of variable-crown or adjustable-crown rolls of the type described above are known. Generally, the nips formed by such rolls, such as press nips or calendering nips, are loaded by means of loading forces applied to the axle journals of the variable-crown roll and of the counter-roll.
The present invention is directed to such variable-crown rolls that include a series of glide shoes whose glide surfaces act upon the inner surface of the roll mantle and which are at least partly hydrostatically lubricated by means of pressurized fluid passed onto the glide surface from lubricating chambers provided on the glide shoes.
Reference is made to Finnish Patents Nos. 46,278 of Beloit Corporation, 68,709 of Kleinewefers GmbH and 68,886 of JM Voith GmbH with regard to prior art related to the invention.
The components of variable crown rolls that support and load the inner surface of the roll mantle by means of pressurized fluid must fulfill many diverse functions. Components already known in the prior art are not capable of fulfilling all of the requirements at the same time. For example, some of the functions required of such loading components are as follows:
(1) the hydrostatic lubrication of the support or glide shoes as well as of the loading piston and cylinder must be well sealed even under the action of varying load forces and even where changes in the angle between the roll mantle and the stationary axle occur;
(2) the loading pistons of the glide shoes must be able to withstand lateral forces caused by friction;
(3) the loading equipment for the glide shoes must be capable of acting as an articulated joint since the relative positions of the roll mantle being supported and the central stationary axle with respect to each other varies to a considerable extent with varying load forces;
(4) the load pistons of the glide shoes must provide sufficiently large forces in the radial direction of the roll over a range that is sufficiently large in order to support and load the roll mantle;
(5) the thickness of the oil film that lubricates the glide surface of the glide shoes must be controllable; and
(6) the bores provided in the central axle of the variable-crown roll in which the loading pistons are fitted must provide the pistons with a considerable range of radial movement.
As noted above, the known loading piston-glide shoe combinations which load and support the rotatable mantles of variable-crown rolls do not fulfill all of the requirements noted above.